Communication control device for a user station for a serial bus system, and method for communicating in a serial bus system

ABSTRACT

A communication control device for a user station for a serial bus system. The communication control device controls a communication of the user station with at least one other user station of the bus system, and generates a transmission signal for transmission onto a bus of the bus system and/or to receive a signal from the bus. The communication control device generates the transmission signal according to a frame in which bits having a predetermined temporal length are provided. The communication control device is designed to shorten, in comparison to some other bit of the bit sequence, at least one bit in the frame that is situated in a bit sequence of at least two bits having the same logical value, and the communication control device is designed to not shorten bits that are not situated in a bit sequence of at least two bits having the same logical value.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. § 119 ofGerman Patent Application No. DE 102021200080.0 filed on Jan. 7, 2021,which is expressly incorporated herein by reference in its entirety.

FIELD

The present invention relates to a communication control device for auser station for a serial bus system, and a method for communicating ina serial bus system that operates with a high data rate and a high levelof error robustness.

BACKGROUND INFORMATION

Bus systems for the communication between sensors and control units, forexample in vehicles, are intended to allow the transfer of a large datavolume, depending on the number of functions of a technical facility ora vehicle. In many applications, it is necessary to transfer the datafrom the sender to the receiver at the highest possible data transferrate.

At the present time, in vehicles, a bus system is used in theintroduction phase, in which data are transferred as messages under theISO 11898-1:2015 standard, as a CAN protocol specification with CAN FD.The messages are transferred between the bus users of the bus system,such as the sensor, control unit, transducer, etc. For this purpose, themessage is transmitted onto the bus in a frame, in which a switch ismade between two communication phases. In the first communication phase(arbitration), it is negotiated which of the user stations of the bussystem is allowed to transmit its frame onto the bus in the subsequentsecond communication phase (data phase or transmission of the usefuldata). With most manufacturers, CAN FD is used in the vehicle at a 500kbit/s arbitration bit rate and a 2 Mbit/s data bit rate in the firststep. During the transfer, a switch is thus to be made back and forth onthe bus between a slow operating mode and a fast operating mode.

To allow even higher data rates in the second communication phase, atthe present time a successor bus system for CAN FD (referred to as CANXL) is being developed, which is presently standardized by the CAN inAutomation (CiA) organization. In addition to strict data transport, CANXL is intended to also support other functions via the CAN bus, such asfunctional safety, data security, and quality of service (QoS). Theseare basic properties that are required in an autonomously travelingvehicle.

Errors may occur during the transfer of data in a frame via a channel(CAN bus). For example, a bit may be falsified or edges between bits maybe shifted due to external influences, in particular irradiation orreflections at bus ends. In addition, as the result of nonideal clocksources, a phase error may occur in a user station, which for thepresent communication on the bus is not a sender, but instead, only areceiver of the message (reception node).

These frame conditions contribute to a reduction in the quantity of datathat is effectively transferable per unit of time (the net data rate).

SUMMARY

An object of the present invention is to provide a communication controldevice for a user station for a serial bus system, and a method forcommunicating in a serial bus system, which solve the above-mentionedproblems. In particular, an object is to provide a communication controldevice for a user station for a serial bus system, and a method forcommunicating in a serial bus system in which a high level of errorrobustness of the communication is achievable, even for a high data rateand optionally an increase in the quantity of the useful data per frame.

The object may be achieved by a communication control device for a userstation for a serial bus system, in accordance with an exampleembodiment of the present invention. In accordance with an exampleembodiment of the present invention, the communication control device isdesigned to control a communication of the user station with at leastone other user station of the bus system, and to generate a transmissionsignal for transmission onto a bus of the bus system and/or to receive asignal from the bus, the communication control device being designed togenerate the transmission signal according to a frame in which bitshaving a predetermined temporal length are provided, the communicationcontrol device being designed to shorten, in comparison to some otherbit of the bit sequence, at least one bit in the frame that is situatedin a bit sequence of at least two bits having the same logical value,and the communication control device being designed to not shorten bitsthat are not situated in a bit sequence of at least two bits having thesame logical value.

Due to the embodiment of the communication control device, it ispossible to transfer more data per unit of time via the bus thanpreviously without reducing the error robustness of the communication inthe bus system.

With the communication control device, in a serial bus system, inparticular for CAN or CAN FD or CAN XL, a robust communication may stillbe made possible with a further increased data rate.

By use of the communication control device in the bus system, it ispossible to maintain an arbitration from CAN in a first communicationphase and still increase the transfer rate considerably compared to CANor CAN FD or CAN XL.

The method carried out by the communication control device may also beused when at least one CAN user station and/or at least one CAN FD userstation that transmit(s) messages according to the CAN protocol and/orCAN FD protocol are/is present in the bus system.

Advantageous further embodiments of the communication control device aredisclosed herein.

Each bit is possibly divided into four segments over time withoutshortening, a first sampling point being provided between the firstsegment and the second segment, and a second sampling point beingprovided between the third segment and the fourth segment, and thecommunication control device being designed to use the first and secondsampling points for determining the logical value of the bit in areception signal which the communication control device receives for thetransmission signal that is transferred via the bus.

Two segments may be situated between the first sampling point and thesecond sampling point without shortening the bit.

According to one exemplary embodiment of the present invention, thecommunication control device may be designed to shorten the second bitof the bit sequence and each subsequent bit of the bit sequence.

According to one exemplary embodiment of the present invention, thecommunication control device may be designed to shorten the segment inthe second bit of the bit sequence directly preceding the secondsampling point and each subsequent bit in the bit sequence, thecommunication control device being designed to shorten the segment inthe second bit of the bit sequence situated directly after the secondsampling point and each subsequent bit in the bit sequence less than thesegment in the last bit of the bit sequence situated directly after thesecond sampling point.

The communication control device may be designed to shorten a bit,situated between a first bit and a last bit of the bit sequence, morethan the last bit of the bit sequence.

According to one exemplary embodiment of the present invention, thecommunication control device is designed to shorten the last bit of thebit sequence more than the first bit of the bit sequence.

According to another embodiment of the present invention, thecommunication control device may be designed to individually determinefor the bit the length of a shortening of a bit of the bit sequence.

It is possible for the communication control device to include anevaluation block for evaluating whether a bit sequence of at least twobits having the same logical value is present in a transmission signalthat is generated by the communication control device, and a bit lengthshortening block for shortening at least one bit in the bit sequencethat has been determined by the evaluation block during the evaluation.

The communication control device may include a bit length lengtheningblock for lengthening at least one bit in the bit sequence, which iscontained as a shortened bit in a signal that is received from the bus.Additionally or alternatively, the communication control device mayinclude an error frame counting block for counting error frames that arereceived from the bus.

In addition, the communication control device may be designed to insertat least one predetermined bit into the transmission signal whichindicates to a reception node in the bus system that a signal presentlyreceived from the bus includes at least one bit that is situated in abit sequence of at least two bits having the same logical value, and isshortened in comparison to some other bit of the bit sequence.

The communication control device may be designed to generate thetransmission signal in such a way that for a message that is exchangedbetween user stations of the bus system, the bit time of a signaltransmitted onto the bus in the first communication phase may bedifferent from a bit time of a signal transmitted in the secondcommunication phase, and in the first communication phase, it isnegotiated which of the user stations of the bus system in thesubsequent second communication phase obtains, at least temporarily,exclusive, collision-free access to the bus, and the communicationcontrol device being designed to shorten at least one bit of a bitsequence, which includes at least two bits having the same logicalvalue, in the first and/or second communication phase.

The frame that is formed for the message may have a design that iscompatible with CAN FD and/or CAN XL.

The communication control device described above may be part of a userstation for a bus system that also includes a transceiver device fortransmitting the transmission signal onto the bus of the bus system, thetransceiver device being designed to transmit the entire frame onto thebus in an operating mode for transmitting and receiving the frame in thefirst communication phase.

The user station described above may be part of a bus system which alsoincludes a bus and at least two user stations that are connected to oneanother via the bus in such a way that they may communicate seriallywith one another. At least one of the at least two user stations is auser station described above.

Moreover, the object stated above may be achieved by a method forcommunicating in a serial bus system according to an example embodimentof the present invention. In accordance with an example embodiment ofthe present invention, the method is carried out using a communicationcontrol device for a user station of the bus system, the methodincluding the steps: controlling, via the communication control device,a communication of the user station with at least one other user stationof the bus system, and for generating a transmission signal fortransmission onto a bus of the bus system and/or receiving a signal fromthe bus, the communication control device generating the transmissionsignal according to a frame in which bits having a predeterminedtemporal length are provided, the communication control deviceshortening in the frame, in comparison to some other bit of the bitsequence, at least one bit that is situated in a bit sequence of atleast two bits having the same logical value, and the communicationcontrol device not shortening bits that are not situated in a bitsequence of at least two bits having the same logical value.

The method yields the same advantages as stated above with regard to theuser station.

Further possible implementations of the present invention also includecombinations, even if not explicitly stated, of features or specificembodiments described above or discussed below with regard to theexemplary embodiments. Those skilled in the art will also add individualaspects as enhancements or supplements to the particular basic form ofthe present invention, in view of the disclosure herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below withreference to the figures, and based on exemplary embodiments.

FIG. 1 shows a simplified block diagram of a bus system according to afirst exemplary embodiment of the present invention.

FIG. 2 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to thefirst exemplary embodiment of the present invention.

FIG. 3 shows a simplified schematic block diagram of a user station ofthe bus system according to the first exemplary embodiment of thepresent invention.

FIG. 4 shows a temporal profile of bus signals CAN XL H and CAN XL L forthe user station according to the first exemplary embodiment of thepresent invention.

FIG. 5 shows a temporal profile of a differential voltage VDIFF of bussignals CAN XL H and CAN XL L for the user station according to thefirst exemplary embodiment of the present invention.

FIG. 6 shows a temporal profile of a portion of a signal that occursduring transmission of a frame to terminals of the user stationaccording to the first exemplary embodiment, when a bit lengthadaptation module is not active.

FIG. 7 shows a temporal profile of a portion of a signal that occursduring transmission of a frame to terminals of the user stationaccording to the first exemplary embodiment, when a bit lengthadaptation module is active.

FIG. 8 shows a temporal profile of a portion of a signal that occursduring transmission of a frame to terminals of the user stationaccording to a second exemplary embodiment, when the bit lengthadaptation module is active.

FIG. 9 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to afourth exemplary embodiment of the present invention.

FIG. 10 shows a diagram for illustrating the design of a message thatmay be transmitted from a user station of the bus system according to afifth exemplary embodiment of the present invention.

Unless stated otherwise, identical or functionally equivalent elementsare provided with the same reference numerals in the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows as an example a bus system 1 that is in particular thebasis for the design of a CAN bus system, a CAN FD bus system, a CAN XLbus system, and/or modifications thereof, as described below. Bus system1 may be used in a vehicle, in particular a motor vehicle, an aircraft,etc., or in a hospital, and so forth.

In FIG. 1, bus system 1 includes a plurality of user stations 10, 20,30, each of which is connected to a first bus wire 41 and a second buswire 42 at a bus 40. Bus wires 41, 42 may also be referred to as CAN Hand CAN L or CAN XL H and CAN XL L, and are used for electrical signaltransfer after coupling in the dominant levels or generating recessivelevels or other levels for a signal in the transmission state. Messages45, 46 in the form of signals are serially transferable betweenindividual user stations 10, 20, 30 via bus 40. If an error occursduring the communication on bus 40, as illustrated by the serrated darkblock arrow in FIG. 1, an error frame 47 (error flag) may optionally betransmitted. User stations 10, 20, 30 are, for example, control units,sensors, display devices, etc., of a motor vehicle.

As shown in FIG. 1, user station 10 includes a communication controldevice 11, a transceiver device 12, and a bit length adaptation module15. User station 20 includes a communication control device 21, atransceiver device 22, and optionally a bit length adaptation module 25.User station 30 includes a communication control device 31, atransceiver device 32, and a bit length adaptation module 35.Transceiver devices 12, 22, 32 of user stations 10, 20, 30 are eachdirectly connected to bus 40, although this is not illustrated in FIG.1.

Communication control devices 11, 21, 31 are each used for controlling acommunication of particular user station 10, 20, 30 via bus 40 with atleast one other user station of user stations 10, 20, 30 connected tobus 40.

Communication control devices 11, 31 create and read first messages 45,which are modified CAN messages 45, for example. Modified CAN messages45 are built up based on a CAN XL format, described in greater detailwith reference to FIG. 2, and in which particular bit length adaptationmodule 15, 35 is used. Communication control devices 11, 31 may also bedesigned to provide a CAN XL message 45 or a CAN FD message 46 fortransceiver device 32 or receive it from same, as needed. Particular bitlength adaptation modules 15, 35 may also be used. Communication controldevices 11, 31 thus create and read a first message 45 or second message46, first and second messages 45, 46 differing by their datatransmission standard, namely, CAN XL or CAN FD in this case.

Communication control device 21 may be designed as a conventional CANcontroller according to ISO 11898-1:2015, i.e., as a CAN FD-tolerantconventional CAN controller or a CAN FD controller. In addition, bitlength adaptation module 25, which has the same function as bit lengthadaptation modules 15, 35, is optionally present. Communication controldevice 21 creates and reads second messages 46, for example CAN FDmessages 46. CAN FD messages 46 may include 0 to 64 data bytes, whichare also transferred at a much faster data rate than with a conventionalCAN message. In particular, communication control device 21 is designedas a conventional CAN FD controller.

Transceiver device 22 may be designed as a conventional CAN transceiveraccording to ISO 11898-1:2015 or as a CAN FD transceiver. Transceiverdevices 12, 32 may be designed to provide messages 45 according to theCAN XL format or messages 46 according to the present CAN FD format forassociated communication control device 11, 31 or receive the messagesfrom same, as needed.

A formation and then transfer of messages 45 having the CAN XL format,in addition to the reception of such messages 45, is achievable by useof the two user stations 10, 30.

FIG. 2 shows for message 45 a CAN FX frame 450, which in particular is aCAN XL frame and which is provided by communication control device 11for transceiver device 12 for transmitting onto bus 40. In the presentexemplary embodiment, communication control device 11 creates frame 450so as to be compatible with CAN FD. The same analogously applies forcommunication control device 31 and transceiver device 32 of userstation 30.

According to FIG. 2, for the CAN communication on bus 40, frame 450 isdivided into different communication phases 451, 452, namely, anarbitration phase 451 and a data phase 452. Frame 450, after a start bitSOF, includes an arbitration field 453, a control field 454, a datafield 455, a check sum field 456, and a frame termination field 457.

In arbitration phase 451, with the aid of an identifier ID including,for example, bits ID28 through ID18 in arbitration field 453, bitwisenegotiation is carried out between user stations 10, 20, 30 concerningwhich user station 10, 20, 30 would like to transmit message 45, 46having the highest priority, and therefore for the next time period fortransmitting in subsequent data phase 452 obtains exclusive access tobus 40 of bus system 1. A physical layer, similarly as with CAN and CANFD, is used in arbitration phase 451. The physical layer corresponds tothe bit transfer layer or layer one of the Open Systems Interconnection(OSI) model.

An important point during phase 451 is that the conventional CSMA/CRmethod is used, which allows simultaneous access of user stations 10,20, 30 to bus 40 without destroying higher-priority message 45, 46. Itis thus possible to add further bus user stations 10, 20, 30 to bussystem 1 in a relatively simple manner, which is very advantageous.

Consequently, the CSMA/CR method must provide so-called recessive stateson bus 40, which may be overwritten by other user stations 10, 20, 30with dominant states on bus 40. In the recessive state, high-impedanceconditions prevail at individual user station 10, 20, 30, which incombination with the parasites of the bus wiring result in longer timeconstants. This results in a limitation of the maximum bit rate of thepresent-day CAN FD physical layer to approximately 2 megabits per secondat the present time during actual vehicle use.

In data phase 452, in addition to a portion of control field 454, theuseful data of the CAN XL frame or of message 45 from data field 455 andcheck sum field 456 are transmitted. Check sum field 456 may contain acheck sum of the data of data phase 452, including the stuff bits, whichare inserted as an inverse bit by the sender of message 45, in each caseafter a predetermined number of identical bits, in particular 10identical bits. At the end of data phase 452, a switch is made back intoarbitration phase 451.

At least one acknowledge bit may be contained in an end field in frametermination phase 457. In addition, a sequence of 11 identical bits thatindicate the end of CAN XL frame 450 may be present. By use of the atleast one acknowledge bit, it may be communicated whether or not areceiver has found an error in received CAN XL frame 450 or message 45.

A sender of message 45 starts a transmission of bits of data phase 452onto bus 40 only after user station 10, as the sender, has won thearbitration, and user station 10, as the sender, thus has exclusiveaccess to bus 40 of bus system 1 for the transmission.

In a bus system with CAN XL, proven properties that are responsible forthe robustness and user-friendliness of CAN and CAN FD, in particular aframe structure including identifiers and arbitration according to theCSMA/CR method, are taken on. Thus, in arbitration phase 451, userstation 10 partially uses as the first communication phase, inparticular up to and including the FDF bit, a format from CAN/CAN FDaccording to ISO 11898-1:2015. However, in comparison to CAN or CAN FD,in data phase 452 as the second communication phase, increasing the netdata transfer rate, in particular to approximately 10 megabits persecond, is possible. In addition, increasing the quantity of the usefuldata per frame to approximately 2 kbytes or an arbitrary value ispossible.

FIG. 3 shows the basic design of user station 10 together withcommunication control device 11, transceiver 12, and bit lengthadaptation module 15, which is part of communication control device 11.User station 20 has a basic design similar to that shown in FIG. 3,except for the differences stated above. User station 30 has a designsimilar to that shown in FIG. 3, except that bit length adaptationmodule 35 according to FIG. 1 is situated separately from communicationcontrol device 31 and transceiver device 32. Therefore, user station 30is not separately described.

According to FIG. 3, in addition to communication control device 11 andtransceiver device 12, user station 10 includes a microcontroller 13with which control device 11 is associated, and a systemapplication-specific integrated circuit (ASIC) 16, which alternativelymay be a system base chip (SBC) on which multiple functions necessaryfor an electronics assembly of user station 10 are combined. In additionto transceiver device 12, an energy supply device 17 that suppliestransceiver device 12 with electrical energy is installed in system ASIC16. Energy supply device 17 generally supplies a voltage CAN_Supply of 5V. However, depending on the requirements, energy supply device 17 maysupply some other voltage having a different value. Additionally oralternatively, energy supply device 17 may be designed as a powersource.

Bit length adaptation module 15 includes an evaluation block 151 thatevaluates transmission signal TxD on bit sequences including bits havingthe same logical value and evaluates reception signal

RxD, a bit length shortening block 152, and optionally a bit lengthlengthening block 153 and an error frame counting block 154. Blocks 151,152, 153, 154 are described in greater detail below.

Transceiver device 12 also includes a transmission module 121 and areception module 122. Even though transceiver device 12 is consistentlyreferred to below, it is alternatively possible to provide receptionmodule 122 in a separate device externally from transmission module 121.Transmission module 121 and reception module 122 may be designed as aconventional transceiver device 22. Transmission module 121 may inparticular include at least one operational amplifier and/or onetransistor. Reception module 122 may in particular include at least oneoperational amplifier and/or one transistor.

Transceiver device 12 is connected to bus 40, or more precisely, to itsfirst bus wire 41 for CAN_H or CAN XL_H and its second bus wire 42 forCAN_L or CAN XL_L. The supplying of voltage for energy supply device 17for supplying first and second bus wires 41, 42 with electrical energy,in particular with voltage CAN Supply, takes place via at least oneterminal 43. The connection to ground or CAN_GND is achieved via aterminal 44. First and second bus wires 41, 42 are terminated via aterminating resistor 49.

In transceiver device 12, first and second bus wires 41, 42 are not justconnected to transmission module 121, also referred to as a transmitter,but also to reception module 122, also referred to as a receiver, eventhough the connection in FIG. 3 is not shown for simplification.

During operation of bus system 1, transmission module 121 converts atransmission signal TXD or TxD of communication control device 11 intocorresponding signals CAN XL_H and CAN XL_L for bus wires 41, 42, andtransmits these signals CAN XL_H and CAN XL_L onto bus 40 at theterminals for CAN_H and CAN_L, as shown in FIG. 4.

According to FIG. 4, reception module 122 forms a reception signal RXDor RxD from signals CAN XL_H and CAN XL_L that are received from bus 40,and passes it on to communication control device 11, as shown in FIG. 3.With the exception of an idle or standby state, transceiver device 12with reception module 122 during normal operation always listens to atransfer of data or messages 45, 46 on bus 40, in particular regardlessof whether or not transceiver device 12 is the sender of message 45.

According to the example from FIG. 4, signals CAN XL_H and CAN XL_L, atleast in arbitration phase 451, include dominant and recessive buslevels 401, 402, as from CAN. A difference signal VDIFF=CAN XL_H−CANXL_L, shown in FIG. 5 for arbitration phase 451, is formed on bus 40.The individual bits of signal VDIFF with bit time t_bt1 may berecognized in arbitration phase 451 using a reception threshold T_a of0.7 V, for example. In data phase 452 the bits of signals CAN XL_H andCAN XL_L are transmitted more quickly, i.e., with a shorter bit timet_bt2, than in arbitration phase 451. Thus, signals CAN XL_H and CANXL_L in data phase 452 differ from conventional signals CAN_H and CAN_L,at least in their faster bit rate.

The sequence of states 401, 402 for signals CAN XL_H, CAN XL_L in FIG. 4and the resulting pattern of voltage VDIFF from FIG. 5 are used only forillustrating the function of user station 10. The sequence of datastates for bus states 401, 402 is selectable as needed.

In other words, transmission module 121, when it is switched into afirst operating mode B_451 (SLOW), according to FIG. 4 generates a firstdata state as bus state 402 with different bus levels for two bus wires41, 42 of the bus line, and a second data state as bus state 401 withthe same bus level for the two bus wires 41, 42 of the bus line of bus40.

In addition, transmission module 121 transmits the bits onto bus 40 at ahigher bit rate for the temporal profiles of signals CAN XL_H, CAN XL_Lin a second operating mode B_452_TX (FAST_TX), which includes data phase452. CAN XL_H and CAN XL_L signals may also be generated in data phase452 with a different physical layer than with CAN FD. The bit rate indata phase 452 may thus be increased even further than with CAN FD. Auser station that is not a sender of frame 450 in data phase 452 sets athird operating mode B_452_RX (FAST_RX) in its transceiver device.

Bit length adaptation module 15 from FIG. 3 is active when user station10 acts as sender and/or receiver of frame 450. Bit length adaptationmodule 15, in particular its evaluation block 151, evaluates the bitsequences in frame 450 before communication control device 11 passes ona TxD signal as a TxD_TC signal at terminal TXD to transceiver device 12for transmission onto bus 40. In addition, bit length adaptation module15, in particular its bit length shortening block 152, may shorten bitsof the TxD signal for the TxD_TC signal when a bit sequence of at leastthree bits having the same logical value occurs in the TxD signal, asdescribed in greater detail below.

The method carried out by bit length adaptation module 15 isparticularly suitable for data phase 452, where one of user stations 10,20, 30 has exclusive access to bus 40 in order to transmit one ofmessages 45, 46, in particular as frame 450. However, bit lengthadaptation module 15 may alternatively or additionally use the method inarbitration phase 451.

FIG. 6 shows, as a function of time t, an example of a difference signalVDIFF that has formed due to a digital transmission signal TxD on bus40. Transmission signal TxD may be generated either according to frame450 or according to the protocol for CAN FD.

The bit sequence shown includes six bits, namely, bits B1 through B6.Bits B1 through B6 have bit length t_bt2, for example, i.e., bits ofdata phase 452. However, the bit sequence may occur in an arbitraryportion of frame 450. The bit sequence may thus occur in first and/orsecond communication phase 451, 452 of a frame 450. Transmission signalTxD is generated by communication control device 11 as the sender offrame 450, is modified in bit length adaptation module 152 as describedin greater detail below, and is then serially transmitted astransmission signal TxD_TC to transceiver device 12.

Each bit of bits B1 through B6 has the same design. Each bit of signalVDIFF, and thus also bits B1 through B6, is/are divided over time t intofour segments SY, P1, PP, P2. A sampling point TP is provided betweenfirst segment SY and second segment PP. In addition, each bit of signalVDIFF is divided over time t into a plurality of time quanta TQ, eachhaving the same length. The number of time quanta TQ is the same in allbits. Time quanta TQ are associated with individual segments SY, PP, P1,P2, segments SY, PP, P1, P2 over time t having different lengths, inother words, having different numbers of time quanta TQ. In the exampleof FIG. 6, segments P1, P2 over time t each have the same length. Inother words, segments P1, P2 have the same number of time quanta TQ.

A synchronization segment SY having the length of one time quantum TQ isprovided at the start of a bit B1 through B6. This is followed by apropagation segment PP that includes multiple time quanta TQ. A firstsampling point TP for sampling the bit is situated between segment SYand segment PP. Segment PP is followed by a first phase P1 prior to asecond sampling point TP for sampling the bit. Second sampling point TPis followed by a second phase P2. If a transition between two differentlogical values occurs in transmission signal TxD, i.e., between 1 and 0or between 0 and 1, a reception node or receiver of frame 450 may checkwhether or not the transition occurs at an expected time. If thetransition does not occur at the expected time, which is at the start ofthe bit, the receiver of frame 450 may compute the time difference andadjust the temporal length of phase P1 or the temporal length of phaseP2, depending on the result. In this way, the receiver may continuouslysynchronize with the time clocking of the transmission node or sender offrame 450. This reduces errors that occur due to irradiation on bus 40(physical layer effects).

Communication control device 11 is designed to sample, in a signal RxDreceived from bus 40, a bit B1 through B6 at first sampling point TP andat second sampling point TP, each of which is situated between two ofsegments SY, PP, P1, P2.

In the example from FIG. 6, difference signal VDIFF alternates itsvoltage level U between values of approximately +2 V and −2 V. Thechange is determined by digital transmission signal TxD or TxD_TC, whichis coupled into bus 40 and alternates between the logical bit values 0and 1. Overshootings of difference signal VDIFF occur in each case atthe changes between the bit values 0 and 1 or 1 and 0. The particularvalue of a bit B1 through B6 of difference signal VDIFF is ascertainedin transceiver device 12 by comparing to a threshold value voltage U_THof reception threshold T a. Transceiver device 12 forms reception signalRxD in the process. If voltage level U of difference signal VDIFF isbelow threshold value voltage U_TH, difference signal VDIFF correspondsto the logical value 0 of digital transmission signal TxD. If voltagelevel U of difference signal VDIFF is above threshold value voltageU_TH, difference signal VDIFF corresponds to the logical value 1 ofdigital transmission signal TxD. In the ideal case, the logical valuesof reception signal RxD correspond to the logical values of transmissionsignal TxD. Otherwise, an error is present.

When user station 10 creates transmission signal TxD from FIG. 6, bitlength adaptation module 15, in particular its evaluation block 151,recognizes a bit sequence 111 after a bit value 0 in signal TxD. Bitsequence 111 is formed from three bits B1 through B3. Bit lengthadaptation module 15, in particular its evaluation block 151,subsequently recognizes a bit sequence 000 in signal TxD. Bit sequence000 is formed from three bits B4 through B6.

Thus, for both bit sequences, in each case three bits having the samelogical value are present in digital transmission signal TxD. Bit lengthshortening block 152 may thus shorten the bit sequence, as illustratedin FIG. 7. This is carried out by bit length adaptation module 15 asfollows.

Evaluation block 151 checks at which bit of bits B1 through B6 oftransmission signal TxD a change in the logical value takes place at thestart or at the end of the bit. For this purpose, evaluation block 151checks, for example, when an edge occurs between two bits. If three ormore bits having the same logical value are transferred, the bits thatare not situated at the edges of the bit sequence may be transmitted inshortened form. In other words, based on the evaluation result ofevaluation block 151, bit length shortening block 152 shortens the bitsthat include no edge (bit value change) at the start or at the end ofthe bit.

For the case of FIG. 7, in first bit sequence 111 from FIG. 7, bitlength shortening block 152 has therefore shortened bit B2. Bit lengthshortening block 152 omits segment PP for bit B2. The lengths of bitsB1, B3 are unchanged in each case. In addition, in second bit sequence000 from FIG. 7, bit length shortening block 152 has shortened bit B5.Bit length shortening block 152 omits segment PP for bit B2 [sic; B5].The lengths of bits B4, B6 are unchanged in each case.

Bit length shortening block 152 carries out a similar procedure, forexample, for a sequence of 5 bits having the same logical value intransmission signal TxD. In this case, the second through fourth bit ofthe bit sequence of five bits is shortened in each case by segment PP.In contrast, the lengths of the first and fifth bit of the bit sequenceare unchanged.

The shortening is very advantageous for bits B2, B4 in the example fromFIGS. 6 and 7, since without a state change or edge between two bits, nophysical layer effects occur. Thus, no irradiations are caused at bus 40which could result in errors in signal VDIFF on bus 40. Since segment PPis the dominating portion of a bit B1 through B6 in terms of length ortime, bit length adaptation module 15 may greatly reduce the bit rate.For high bit rates of 5 Mbit/s, over one-half of bit time t_bt1, t_bt2may be saved. This may mean up to a doubling of the bit rate.

In general, bit length adaptation module 15 may be set to shorten thebits of a bit sequence when more than one bit having the same logicalvalue is to be transmitted onto bus 40. In this case as well,disturbances and errors can no longer act on these bits.

In contrast, if user station 10 is a receiving user station of bussystem 1, which at the present time is not a sender of frame 450, butinstead only receives frame 450 (reception node), user station 10 viaits evaluation block 151 recognizes the shortened bit length by samplingat sampling points TP of reception signal RxD. In particular,communication control device 11 samples reception signal RxD after eachtime quantum TQ. As a result, a reception node may correctly sample thebits of signal VDIFF according to FIG. 7 which the reception nodereceives from bus 40 at its terminals CAN_H, CAN_L. Optionally, bitlength lengthening block 153 may once again lengthen the bits ofreception signal RxD, recognized as shortened, to the normal length.Alternatively, communication control device 11 evaluates receptionsignal RxD. In particular, communication control device 11 samplesreception signal RxD after each time quantum TQ, but using the bitshaving different lengths.

By use of this embodiment of user stations 10, 20, 30 of bus system 1,more bits may be transferred via bus 40 in the same time period. Thedata rate in bus system 1 is thus increased.

If a user station 10, 20, 30 that does not understand the bit timeshortening is to be at bus 40, this user station 10, 20, 30 will disturbthe communication in bus system 1 via error frames 47 when one of bitlength adaptation modules 15, 25, 35 is active for a transmission signalTxD. In such a case, error frame counting block 154 counts error frames47 received from bus 40. Beginning at a certain number of error frames47, evaluation block 151 evaluates that the method is no longer used forshortening at least one bit of a bit sequence. Instead, communicationcontrol device 11 then uses only the conventional protocol, in which noshortening of bits is used. Associated bit length adaptation module 15,25, 35 of user station 10, 20, 30 is thus deactivated.

A robust emergency operation of the communication in bus system 1 isthus possible. This is advantageous in particular when bus system 1 isused in a vehicle. The emergency operation is then ensured, for example,while the vehicle is traveling.

Communication control device 11, in particular its evaluation block 151,may reduce the count value of error frame counting block 154 when amessage 45 that includes at least one shortened bit of a bit sequence issuccessfully sent. In this way, sporadic errors that are not caused byan incompatibility of the communication protocols of user station 10,20, 30 at bus 40 do not result in a reduction in the possibletransferable baud rate in bus system 1.

In contrast, for a software update of the vehicle in a repair shop, itmay be desired to work using the highest possible data rate. This may bethe case when the data of the new software are of interest only for anindividual user station at bus 40. For such a case, it is possible for arepair shop tester to use the above-described method for shortening bitsin a targeted manner during the transmission of messages 45, 46 in bus40 until the incompatible user station(s) prevent(s) the transmission oferror frames 47 and go(es) into an error state of exception. Beginningat this point in time, communication control device 11 may use theabove-described described method for shortening at least one bit of abit sequence undisturbed during the transmission of messages 45, 46according to FIG. 7. The software update may thus be transferred in ashorter time than with conventional messages 45, 46 including bits ofnormal length, as shown in FIG. 6.

According to one modification of the present exemplary embodiment, bitlength adaptation module 15 additionally or alternatively shortens thefirst or last bit of a bit sequence having the same logical value, forexample bit B1 or bit B3 of first bit sequence 111 in FIG. 6. However,an additional shortening of the first or last bit of a bit sequencehaving the same logical value is usually more advantageous than analternative shortening for increasing the net data rate in bus system 1.

At the edge of the bit, the first bit as well as the last bit of the bitsequence has only a single edge with which the reception nodesynchronizes. For the shortening, bit length adaptation module 15 mayshorten segment PP or may omit it. Bit length adaptation module 15assumes that the synchronization edge at the start or end of a bit isperfect by definition. In such a case, no physical layer effects are tobe taken into account or tolerated, or fewer physical layer effectsoccur, for this bit at the start or end of the bit sequence. Segment PPmay thus be shortened or omitted also for this bit at the start or endof the bit sequence.

For a CAN-based bus system, communication control device 11 synchronizesitself with the increasing differential voltage that occurs during achange from a bit having logical value 1 to a bit having logical value0. Therefore, for a bit sequence 0111110, bit length adaptation module15, in particular its block 152, could shorten the second through fifthbits of bit sequence 11111. For bit sequence 1000001, bit lengthadaptation module 15, in particular its block 152, could shorten thefirst through fourth bits of bit sequence 00000.

Alternatively, it is possible for bit length adaptation module 15 toshorten only the first bit or the last bit of a bit sequence having thesame logical value.

The described modification and its alternative allow an even higher datarate than with the exemplary embodiment described above.

According to another modification of the present exemplary embodiment,bit length adaptation module 15 individually shortens segment PP of oneof the bits described above. For example, bit length adaptation module15 may shorten segment PP of one of the above-described bits as afunction of which of the transitions take place in the bit. Bit lengthadaptation module 15 may thus individually reduce the value of theshortening of segment PP as a function of whether a transition from 0 to1 or from 1 to 0 takes place. In addition, the shortening of segment PPof a bit between the start bit and end bit of the bit sequence may havesome other value. For bit sequence 111 from FIG. 7, bit lengthadaptation module 15 could, for example, shorten bit B1 by ⅓ the lengthof segment PP from FIG. 6, while shortening bit B2 by ½ the length ofsegment PP from FIG. 6.

The modification for the individual shortening of the bits isadvantageous in particular when differential voltages of 0 volt and 2volts are used, and in particular when a change is made between dominantand recessive bits. In this case, the distortion of the edges betweenthe bits may differ greatly. The difference is [based on] whether thedifferential voltage goes or changes from 2 volts to 0 volt or from 0volt to 2 volts.

Therefore, bit length adaptation module 15 may select segment PPindividually for each of the two transitions. Additionally oralternatively, bit length adaptation module 15 may individuallyestablish the shortening of segment PP if no transition takes place,depending on which bits in the same sequence are transferred.

The described modifications and their alternatives, when additionallyapplied, in each case allow an even higher data rate than with theexemplary embodiment described above.

FIG. 8 shows a signal VDIFF on bus 40 that is formed by bit lengthadaptation module 15 according to a second exemplary embodiment. Forthis purpose, bit length adaptation module 15 carries out a method thatdiffers from the method according to the preceding exemplary embodimentin the following aspects.

As shown in FIG. 8, bit length shortening block 152 is designed toadditionally shorten segments P1, P2 of bits B2, B3 in bit sequence 111that is formed from bits B1 through B3. Bits B2, B3 are the bits in bitsequence 111 for which segment PP is omitted. In addition, in bitsequence 000 of bits B4 through B6, bit length shortening block 152 hasshortened segments P1, P2 of bits B5, B6, which are shortened by segmentPP.

The shortening of at least one bit of bit sequence B1 through B3 in thesignal from FIG. 6 with regard to segments P1, P2, so that the signalfrom FIG. 8 results, is easily possible due to the fact that less phaseerror is accumulated due to shorter bits.

For the shortening of segments P1, P2, bit length shortening block 152takes into account that a synchronization error must not result in thepossibility of a bit that was not transmitted being erroneouslyreceived, or of a bit that was transmitted, erroneously not beingreceived. Bit length shortening block 152 ensures this by dimensioningsegments P1, P2 to be sufficiently large. In FIG. 8, for example segmentP2 of bit B3 is selected to be larger than bit B2 in bit sequence 111.In other words, in the last bit of a bit sequence of bits having thesame logical value, segment P2 is larger than in a bit that is neitherthe first nor the last bit of the bit sequence.

Since segment SY is always present at the start of the bit in each bitof the signal from FIG. 6 and of the signal from FIG. 8, a receptionnode may always make a synchronization for segment SY if necessary.However, when the level of signal VDIFF is unchanged, segment SY is usedonly to establish the unchanged level.

In other respects, the mode of operation of bus system 1 is identical tothe first exemplary embodiment.

According to a third exemplary embodiment, bit length shortening block152 is designed to leave segments P1, P2 in their original length. Inaddition, bit length shortening block 152 is designed to transmit thestuff bits after the same number of time quanta TQ, but to transmit astuff bit only after a greater number of bits than in other portions offrame 450.

In this case, a similar shortening of signal VDIFF may be achieved aswith the second exemplary embodiment, in which at least one of segmentsP1, P2 of a bit B1 through B6 is to be shortened.

As a result, for the third exemplary embodiment a similar net data rateis achievable as for the second exemplary embodiment.

FIG. 9 shows a frame 450A according to a fourth exemplary embodiment.Frame 450A may be used by communication control device 11 to generatetransmission signal TxD and/or to evaluate reception signal RxD, asdescribed above.

In frame 450A, at least one bit B_V is contained in control field 454.The fewer bits B_V that are contained, the less the transferable netdata rate in bus system 1 is lowered.

The at least one bit B_V indicates whether or not bit sequence(s) ofbits having the same logical value in a reception signal RxD, presentlyreceived from bus 40, is/are to be transmitted in shortened form.

Thus, a transmission node may communicate to a reception node at bus 40,which includes the at least one bit B_V, how presently receivedreception signal RxD is to be evaluated. When evaluating presentlyreceived reception signal RxD, the reception node may thus correctlytake into account the shortening of bit sequences that has taken place.

In other words, the use of the above-described method of shortening thebit sequence of bits having the same logical value according to FIG. 7or FIG. 8 may be announced via a reserved bit in the header of a message45.

The downward compatibility with conventional communication protocols, inparticular CAN-based protocols, is thus ensured.

Alternatively, the at least one bit B_V is contained in data field 455.

FIG. 10 shows a frame 450B according to a fifth exemplary embodiment.Frame 450B may be used by communication control device 11 to generatetransmission signal TxD and/or to evaluate reception signal RxD, asdescribed above.

In frame 450B, at least one bit B_V is contained in control field 455.The at least one bit B_V indicates that in a message 45 that is soon tobe transmitted via bus 40, the bit sequence(s) of bits having the samelogical value is/are transmitted in shortened form. Thus, a receptionnode knows whether bit sequence(s) of bits having the same logical valueis/are shortened in a subsequent reception signal RxD, as shown in FIG.7 or FIG. 8.

If more than one bit B_V is contained, it may be communicated whichmessage 45, 46 of the subsequent messages at bus 40 is to be modified insuch a way that the bit sequence(s) of bits having the same logicalvalue is/are shortened. For example, a specific identifier for thismessage 45, 46 may then be encoded in a bit sequence of at least twobits B_V.

A transmission node may thus communicate to a reception node containingbit B_V how reception signal RxD of next message 45, 46 received frombus 40 is to be evaluated. The reception node may thus correctly takeinto account the shortening of bit sequences that has taken place whenevaluating presently received reception signal RxD.

In other words, the use of the above-described method of shortening thebit sequence of bits having the same logical value according to FIG. 7or FIG. 8 may have been announced in a preceding message.

It is possible to use, at least in sections, a shortening of the bitsequence of bits having the same logical value also in the message thathas been created based on a frame 450B.

The downward compatibility with conventional communication protocols, inparticular CAN-based protocols, is thus also ensured.

All of the above-described embodiments of user stations 10, 20, 30, ofbus system 1, and of the method carried out therein may be used alone orin any possible combination. In particular, all features of theabove-described exemplary embodiments and/or modifications thereof maybe arbitrarily combined. Additionally or alternatively, in particularthe following modifications are possible.

Although the present invention is described above with the example ofthe CAN bus system, the present invention may be employed for anycommunications network and/or communication method in which twodifferent communication phases are used in which the bus states, whichare generated for the different communication phases, differ. Inparticular, the present invention is usable for developments of otherserial communications networks, such as 100Base-T1 Ethernet, field bussystems, etc.

In particular, bus system 1 according to the exemplary embodiments maybe a communications network in which data are serially transmittable attwo different bit rates. It is advantageous, but not a mandatoryrequirement, that in bus system 1, exclusive, collision-free access of auser station 10, 20, 30 to a shared channel is ensured, at least forcertain time periods.

The number and arrangement of user stations 10, 20, 30 in bus system 1of the exemplary embodiments is arbitrary. In particular, user station20 in bus system 1 may be dispensed with. It is possible for one ormultiple of user stations 10 or 30 to be present in bus system 1. It ispossible for all user stations in bus system 1 to have the same design,i.e., for only user station 10 or only user station 30 to be present.

What is claimed is:
 1. A communication control device for a user stationfor a serial bus system, the communication control device beingconfigured to: control a communication of the user station with at leastone other user station of the bus system, and generate a transmissionsignal for transmission onto a bus of the bus system and/or receive asignal from the bus; generate the transmission signal according to aframe in which bits having a predetermined temporal length are provided;shorten, in comparison to some other bit of a bit sequence, at least onebit in the frame that is situated in a bit sequence of at least two bitshaving the same logical value, and not shorten bits that are notsituated in the bit sequence of at least two bits having the samelogical value.
 2. The communication control device as recited in claim1, wherein each bit is divided into four segments over time withoutshortening, a first sampling point being provided between a firstsegment of the segments and a second segment of the segments, a secondsampling point being provided between a third segment of the segmentsand a fourth segment of the segments, and wherein the communicationcontrol device configured to use the first and second sampling pointsfor determining a logical value of the bit in a reception signal whichthe communication control device receives for the transmission signalthat is transferred via the bus.
 3. The communication control device asrecited in claim 2, wherein two segments of the segments are situatedbetween the first sampling point and the second sampling point withoutshortening the bit.
 4. The communication control device as recited inclaim 2, wherein the communication control device is configured toshorten a second bit of the bit sequence and each subsequent bit of thebit sequence.
 5. The communication control device as recited in claim 2,wherein the communication control device is configured to shorten asegment in a second bit of the bit sequence directly preceding thesecond sampling point and each subsequent bit in the bit sequence, thecommunication control device being configured to shorten a segment inthe second bit of the bit sequence situated directly after the secondsampling point and each subsequent bit in the bit sequence less than asegment in a last bit of the bit sequence situated directly after thesecond sampling point.
 6. The communication control device as recited inclaim 1, wherein the communication control device is configured toshorten a bit, situated between a first bit and a last bit of the bitsequence, more than the last bit of the bit sequence.
 7. Thecommunication control device as recited in claim 6, wherein thecommunication control device is configured to shorten the last bit ofthe bit sequence more than the first bit of the bit sequence.
 8. Thecommunication control device as recited in claim 1, wherein thecommunication control device is configured to individually determine foreach bit a length of a shortening of the bit of the bit sequence.
 9. Thecommunication control device as recited in claim 1, wherein thecommunication control device includes: an evaluation block configured toevaluate whether the bit sequence of at least two bits having the samelogical value is present in a transmission signal that is generated bythe communication control device; and a bit length shortening blockconfigured to shorten at least one bit in the bit sequence that has beendetermined by the evaluation block during the evaluation.
 10. Thecommunication control device as recited in claim 1, wherein thecommunication control device includes: a bit length lengthening blockconfigured to lengthen at least one bit in the bit sequence, which iscontained as a shortened bit in a signal that is received from the bus,and/or an error frame counting block configured to count error framesthat are received from the bus.
 11. The communication control device asrecited in claim 1, wherein the communication control device isconfigured to insert at least one predetermined bit into thetransmission signal which indicates to a reception node in the bussystem that a signal presently received from the bus includes at leastone bit that is situated in the bit sequence of at least two bits havingthe same logical value, and is shortened in comparison to some other bitof the bit sequence.
 12. The communication control device as recited inclaim 1, wherein the communication control device is configured togenerate the transmission signal in such a way that for a message thatis exchanged between user stations of the bus system, a bit time of asignal transmitted onto the bus in a first communication phase isdifferent from a bit time of a signal transmitted in the secondcommunication phase, and in the first communication phase, it isnegotiated which of the user stations of the bus system in a subsequentsecond communication phase obtains, at least temporarily, exclusive,collision-free access to the bus, and wherein the communication controldevice is configured to shorten at least one bit of the bit sequencewhich includes at least two bits having the same logical value, in thefirst and/or second communication phase.
 13. The communication controldevice as recited in claim 1, wherein the frame that is formed for themessage is compatible with CAN FD and/or CAN XL.
 14. A user station fora serial bus system, comprising: a communication control deviceconfigured to: control a communication of the user station with at leastone other user station of the bus system, and generate a transmissionsignal for transmission onto a bus of the bus system and/or receive asignal from the bus, generate the transmission signal according to aframe in which bits having a predetermined temporal length are provided,shorten, in comparison to some other bit of a bit sequence, at least onebit in the frame that is situated in a bit sequence of at least two bitshaving the same logical value, and not shorten bits that are notsituated in the bit sequence of at least two bits having the samelogical value; and a transceiver device configured to transmitting thetransmission signal onto the bus of the bus system, the transceiverdevice configured to transmit an entire frame onto the bus in anoperating mode for transmitting and receiving the frame in the firstcommunication phase.
 15. A bus system, comprising: a bus; and at leasttwo user stations that are connected to one another via the bus in sucha way that they may communicate serially with one another, at least oneof the user stations including: a communication control deviceconfigured to: control a communication of the user station with at leastone other user station of the bus system, and generate a transmissionsignal for transmission onto the bus and/or receive a signal from thebus, generate the transmission signal according to a frame in which bitshaving a predetermined temporal length are provided, shorten, incomparison to some other bit of a bit sequence, at least one bit in theframe that is situated in a bit sequence of at least two bits having thesame logical value, and not shorten bits that are not situated in thebit sequence of at least two bits having the same logical value; and atransceiver device configured to transmitting the transmission signalonto the bus of the bus system, the transceiver device configured totransmit an entire frame onto the bus in an operating mode fortransmitting and receiving the frame in the first communication phase.16. A method for communicating in a serial bus system, the method beingcarried out using a communication control device for a user station ofthe bus system, the method comprising the following steps: controlling,via the communication control device, a communication of the userstation with at least one other user station of the bus system; andgenerating a transmission signal for transmission onto a bus of the bussystem and/or receiving a signal from the bus, the communication controldevice generating the transmission signal according to a frame in whichbits having a predetermined temporal length are provided, thecommunication control device shortening in the frame, in comparison tosome other bit of a bit sequence, at least one bit that is situated inthe bit sequence at least two bits having the same logical value, andthe communication control device not shortening bits that are notsituated in the bit sequence of at least two bits having the samelogical value.